Saturday, 15 July 2006

Soil Development on Calcareous Rocks in Central Siberia.

Dmitry Ye. Konyushkov, V.V. Dokuchaev Soil Science Institute, Pyzhevskii per. 7, Moscow, 119017, Russia

1. Calcareous rocks of the Pre-Cambrian and Paleozoic ages are widespread in Central Siberia, especially in the northern and southern parts of the Central Siberian Plateau. The bioclimatic conditions in the areas of their development vary from the mountainous Polar desert environment to the tundra and taiga environments, cryosteppes, and true steppes. The humid and semiarid conditions can be distinguished in different temperature belts. Thus, Central Siberia can be considered a model region for studying the specificity of pedogenesis on calcareous substrates under different environmental conditions. The diversity of calcareous substrates is also important.

2. Calcareous bedrocks outcrop to the surface in the areas of highly elevated plateaus, where soils are developed from a relatively thin stony weathered mantle of limestone and dolomite. The lithologic and petrographic specificity of the particular layers of these initially marine deposits should be taken into account in the assessment of the character of pedogenesis. On less elevated plains and lowlands, calcareous bedrock is covered by a mantle of predominantly silicate loamy substrates of uncertain genesis with different amounts of carbonates in the fine earth and inclusions of pebbles and coarse calcareous rock fragments from the underlying bedrock. In the peripheral zones of the elevated plateaus, intrusive bodies of mafic and ultramafic rocks are often found. They occupy the dominant position in the local relief and enrich the surrounding mantle of loose surface deposits with considerable amounts of weatherable minerals. Cryogenic processes In the northern and central parts of Central Siberia are active; sorted patterned ground forms are developed in the areas of calcareous bedrock outcrops; solifluction flows and hummocky microtopography are typical of the areas with a loamy mantle. Paleocryogenic micro- and mesotopography is also widespread, especially in the southern regions. Karst processes are impeded by the presence of permafrost and masked by the cryogenic forms and thermokarst.

3. The Soil Map of the Russian Federation (1988) characterizes the well drained plateaus and ridges with calcareous substrates as the areas of mucky calcareous and tundra mucky calcareous soils in the northern part of Central Siberia and mucky and soddy calcareous soils in its southern part. Less drained positions with loamy calcareous substrates are characterized as the areas of tundra and taiga peat mucky gley soils in complexes with barren spots and "frozen soils of cryogenic cracks" in the northern part and as soddy calcareous soils in the southern part. The analysis of available data suggests that the diversity of soils developed from calcareous parent materials is much greater, and that these soils have their own specificity under different climatic conditions.

4. Among the soils developed from hard calcareous rocks, several groups can be distinguished depending on the character of organic matter accumulation and humification processes. The group of Xero-Calcisols (Xero-Rendzinas) is suggested as the group of soils developed from stony (loamy-stony) calcareous substrates under extremely scarce vegetation in semiarid to arid climatic conditions of different climatic belts; the accumulation of small amounts of plant detritus is typical of them. The admixture of weatherable silicate minerals leads to metamorphic (autochthonous) ferrugination and the development of Pale-Calcareous (Cambi-Calcisols) soils. Additional enrichment of the substrate with nutrients can lead to the development of fertile Soddy-Mucky calcareous soils under herbs in the tundra zone. The soils developed from loamy and heavy loamy calcareous substrates are normally poorly drained in permafrost-affected areas, even under semiarid climatic conditions. Depending on the development of gley features, Peat-Mucky Gleyed and Nongleyed (cryozemic) calcareous soils are distinguished. The ecology of different kinds of soils developed from calcareous substrates is discussed.

5. It is important that under semiarid to arid climatic conditions, especially in permafrost-affected areas (but also beyond them), soils developed from calcareous substrates are usually less fertile and productive than soils developed from silicate substrates. In particular, this is seen from a sharp decrease in the upper tree line in the areas with calcareous substrates in the north of Central Siberia. In the humid regions, the presence of calcareous materials usually improves soil fertility. The reasons for this phenomenon are to be discussed.

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